AJP - Heart and Circulatory Physiology, Vol 258, Issue 3 814-H820, Copyright © 1990 by American Physiological Society
Positive pleural pressure decreases coronary perfusion
H. E. Fessler, R. G. Brower, R. Wise and S. Permutt
Department of Medicine, Johns Hopkins Medical Institutions, Francis Scott Key Medical Center, Baltimore, Maryland 21224.
Pressure surrounding the heart (PSH) rises with maneuvers that increase
pleural pressure. This may decrease left ventricular (LV) oxygen demand by
reducing LV afterload. However, positive PSH may also directly impede
coronary flow. To study the effects of positive PSH on coronary perfusion,
PSH was increased in 10-mmHg increments from 0 to 60 mmHg in an isolated
canine heart-lung preparation with constant venous return, arterial
pressure, and lung volume. Increased PSH caused a rapid significant (P less
than 0.001) fall in left atrial transmural pressure (PLATM) of up to 1.28
+/- 0.31 mmHg. With constant venous return and lung volume, this was
interpreted to reflect decreased LV afterload. However, at levels of PSH
greater than 30 mmHg, initial decreases in PLATM were followed by sustained
increases, suggesting that there was a deterioration in cardiac function
despite the lower level of afterload. Increased PSH was also associated
with decreases in circumflex coronary artery flow [flow (ml/min) = 52.4 -
0.4PSH, P less than 0.01]. Moreover, when the circumflex coronary artery
was maximally dilated with adenosine, the effects of PSH were amplified
[flow (ml/min) = 137.9 - 1.78PSH, P less than 0.001], indicating that
positive PSH mechanically impeded coronary flow. When PSH was raised to 60
mmHg for 90 s, the aortic-coronary sinus lactate concentration difference
fell from 0.71 +/- 0.09 to 0.10 +/- 0.21 mM (mean +/- SE, P less than
0.001, n = 8), suggesting myocardial ischemia. We conclude that positive
PSH directly decreases myocardial perfusion. This may lead to ischemic
cardiac dysfunction, especially in patients with low arterial pressure or
coronary artery disease.
